THE DYNAMICS OF INDIRECT RECIPROCITY

Richard Alexander has argued that moral systems derive from indirect r eciprocity. We analyse a simple case of a model of indirect reciprocit y based on image scoring. Discriminators provide help to those individ uals who have provided help. Even if the help is never returned by the beneficiary, or by individuals who in turn have been helped by the be neficiary, discriminating altruism can be resistant against invasion b y defectors. Indiscriminate altruists can invade by random drift, howe ver, setting up a complex dynamical system. In certain situations, def ectors can invade only if their invasion attempts are sufficiently rar e. We also consider a model with incomplete information and obtain con ditions for the stability of altruism which differ from Hamilton's rul e by simply replacing relatedness with acquaintanceship. (C) 1998 Acad emic Press.